Science & TechnologyPriority2025-07-30

ISRO Launches NASA-ISRO Synthetic Aperture Radar (NISAR)

Why focus: GS3 Sci/Tech flagship. Perfect for Match-the-Following on radar frequencies (L/S band) and 12-day global mapping cycle.

In News

What Happened

On July 30, 2025, the Indian Space Research Organisation (ISRO) successfully launched the NASA-ISRO Synthetic Aperture Radar (NISAR) satellite aboard a GSLV Mk II (GSLV-F16) rocket from the Satish Dhawan Space Centre in Sriharikota. The observatory was deployed into a 747 km Sun-synchronous orbit. It is the world's first Earth observation satellite to carry a dual-frequency (L-band and S-band) radar system.

Why It Matters

Costing approximately $1.5 billion, NISAR represents a historic milestone in Indo-US space cooperation and is the most expensive Earth-imaging satellite ever built. By mapping the entire globe every 12 days and detecting surface movements as small as a single centimetre, it will revolutionize global disaster management, track the impacts of climate change on ice sheets, and monitor the planet's ecosystems.

Background

History & Context

The genesis of the NISAR mission traces back to 2012, when NASA and ISRO began discussions to co-develop an unprecedented radar imaging satellite. The collaboration was formally cemented on September 30, 2014, when NASA Administrator Charles Bolden and ISRO Chairman K. Radhakrishnan signed the official Implementing Arrangement. Under this agreement, NASA's Jet Propulsion Laboratory (JPL) committed to providing the L-band radar and a massive 12-meter deployable mesh antenna, while ISRO agreed to build the S-band radar, the spacecraft bus (based on its I-3K structure), and provide the GSLV Mk II launch vehicle. Despite multiple development delays, the spacecraft completed joint integration at ISRO's UR Rao Satellite Centre in Bengaluru before its flawless launch in July 2025.

What Changed

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BEFORE: Earth-observing radar satellites typically carried only a single radar frequency (either C, L, or S-band), limiting their analytical depth. NOW: NISAR operates the world's first dual-frequency radar, combining NASA's 24-cm L-band (which penetrates deep vegetation) with ISRO's 12-cm S-band (which captures fine surface and urban infrastructure details).
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BEFORE: High-resolution radar satellites often suffered from narrow coverage swaths, meaning it took weeks or months to map the globe. NOW: Utilizing advanced SweepSAR technology, NISAR achieves a wide 242 km imaging swath, enabling a complete mapping of Earth's land and ice surfaces every 12 days.
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BEFORE: Much high-resolution Earth observation data was commercially paywalled or restricted. NOW: Both space agencies have implemented a strict free and open data policy, ensuring data availability within 24 to 48 hours (and even faster for disaster emergencies).
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BEFORE: Detecting minor shifts in the Earth's crust from space was constrained by lower resolution limitations. NOW: NISAR's interferometric SAR capabilities can measure vertical surface deformations as minute as 1 centimetre, providing critical early warnings for volcanic eruptions, landslides, and subsidence.

What Did NOT Change

Despite the groundbreaking nature of the payload, ISRO relied on its tried-and-tested heritage hardware for the satellite's foundation, specifically utilizing the standard I-3K structural bus heavily used in previous INSAT communication satellites. Furthermore, physical ground-truthing remains indispensable; calibration during the science phase still heavily relies on terrestrial corner reflector antennas deployed across locations like Ahmedabad.

Prelims Angle

NCERT Connection

This event directly applies the concepts found in Class 11 'Practical Work in Geography', Chapter 7 - 'Introduction to Remote Sensing'. The chapter explains the difference between active and passive sensors. While optical satellites (passive) depend on solar illumination and are blocked by clouds, NISAR is an active sensor that generates its own microwave pulses. Its dual-frequency synthetic aperture radar demonstrates how active remote sensing can provide continuous, all-weather, day-and-night observation of the Earth's surface.

Common Misconceptions

✗ Because it uses the GSLV rocket and the I-3K bus, NISAR is a heavy communication satellite.

✓ NISAR is strictly an Earth observation and scientific satellite. The I-3K bus, traditionally used for communication satellites, was selected because the massive radar payload requires immense power (6.5 kW) and structural support.

The Geosynchronous Satellite Launch Vehicle (GSLV) and the I-3K bus are almost exclusively associated with India's GSAT/INSAT telecommunication constellation.

✗ NASA and ISRO contributed equally to the $1.5 billion funding of the mission.

✓ NASA bore the vast majority of the mission's cost (approximately $1.1-$1.2 billion), while ISRO's contribution was roughly $96 million (around ₹788 crore).

The mission is heavily promoted as an 'equal partnership', which accurately reflects the shared scientific access and joint engineering effort, but not the financial breakdown.

✗ NISAR is placed into a Geosynchronous orbit because it was launched by the GSLV.

✓ NISAR was injected into a 747 km near-polar, Sun-synchronous Low Earth Orbit (LEO).

The 'G' in GSLV stands for Geosynchronous, leading to the assumption that every payload it carries goes to a high-altitude geosynchronous or geostationary orbit.

Practice Questions

Q1

How Many Correct

Consider the following statements regarding the NASA-ISRO Synthetic Aperture Radar (NISAR) mission: 1. It was injected into a Geosynchronous Transfer Orbit (GTO) by the GSLV Mk II launch vehicle. 2. NASA's L-band radar payload has a longer wavelength than ISRO's S-band payload, allowing it to penetrate dense forest canopies. 3. Data from the mission is kept restricted under the strategic defense protocols of India and the United States. How many of the above statements are correct?

Q2

Match the Following

Match the components/features of the NISAR mission (List I) with their respective providers or properties (List II): List I A. S-band SAR payload B. L-band SAR payload C. Orbit Type D. Antenna Reflector Size List II 1. Sun-synchronous (near-polar) 2. ISRO 3. 12 meters 4. NASA Select the correct code:

Q3

Assertion & Reason

Assertion (A): The NISAR satellite combines both L-band and S-band microwave radar frequencies on a single platform. Reason (R): Optical imaging satellites face severe limitations in providing continuous global data due to heavy cloud cover and the absence of solar illumination at night. Select the correct answer:

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